Originally Posted by alanbikehouston
But, YOU are a metals expert....
And, take photos of the "cut" that show whether the interior of the cut section is "bright and shiny" or corroded and rusty...
...and the interior of the shackle is "instantly" rusty and corroded...well, you would be right, and I'd be wrong.
Most non-stainless steel alloys will rust heavily within 12 hours given the OP's listed conditions (high humidity and/or rain.) Especially if there's rough pitting/scoring from being cut, and quicker if there's any mild acidity to the exposed surfaces. "Instantly" is a bit of a stretch for visibility, but the rusting does begin in that short a time. It just usually takes a few hours before it's visible.
/Manufacturing engineer, re-design and fabrication. I'll post degredation vs. relative humidity and temperature charts if you really want to know how fast different steel alloys rust.
//Seriously,
this is grade-school science fair material. Steel wool in tap water, salt water, vinegar, and water with baking soda.